This invention relates to parking and emergency braking systems applied to drawworks like those used in oil and gas well drilling rig applications.
Drawworks raise or lower traveling equipment and drill strings by reeling in or paying out a cable connected to the drill string's block-and-tackle connection device, typically a travelling block or hook block. The cable has one end fixed to the rig and the other end fixed to the drawworks drum. A drive system (no clutch) turns the drum and AC motors—a component of the drive system—dynamically (regeneratively) brake the drum as the cable is paid out. When static load holding is desired, the brake system stops the drum to hold the drill string at a fixed position.
The drawworks parking/emergency braking system is also designed to function as a limited duty non-cyclical dynamic brake (emergency) when the primary braking system is not functional, in the event of an AC power interruption or other situation whereby power is removed from the drive motors.
Prior art drawworks may use the motor that drives the drum as the primary brake. On the drum itself is a drum-side braking system that acts as both an emergency brake and parking brake. This braking system typically includes two brake discs, one at each side of the drum, and with at least one caliper with brake pads acting on each disc.